Process for dephosphorizing metals



UNITED STATES PATENT orrlcr.

2,123,658 t i PROCESS FOR DEPHOSPHOEIZING METALS i Item? Perrin, Paris, France, assignor to Societc dElectrochimie, dElectrometallurgie et des Acieries Electrlques d'Ugine, Paris, France, a

corporation of France No Drawing. Application April 9, 1936, Serial No. 73,589. In France April 16, 1935 -2 Claims.

The present invention concerns a process for dephosphorizing-pig iron and steels, more particularly hard steels.

In Patent No. 2,015,692 of October 1, 1935, the

cautions it was possible to utilize it for producing a certain intermixing and for producing rapid reactions between slag and metal involving practical results of dephosphorization under conditions of economical interest. I

The applicant has ascertained by successive experiments:-

1. That there is no relation between this phe-' nomenon and the phosphorus content of the proceed, but at this moment the intimate contact of the slag and of the metal has ceased, the density of the metal, having drawn it to the bottom of the-receptacle and from this fact the reduction of the carbon content is limited.

5 applicant has described an extremely rapid procmetal. 5 ess for the dephosphorization of steel in which 2. That with the same slag heated to the same the metal is caused to act upon a basic and temperature the phenomenon is the more violent oxtidizing slag with an energy such that a violent the more carburized the metal.

, in ermixing of the metal and of the slag is caused, 3. That with the same metal at the same temo bringing about a turbulent emulsion of the slag perature the phenomenon is the more violent the in the metal and allowing consequently an almost more oxidized the slag. instantaneous dephosphorization to be obtained 4- That w th t e S m Slag d he Same metal due to the intimate interpenetration of the metal the phenomenon is the more violent the higher and of the slag. the temperature of the reacting elements.

In the above mentioned patent there has been Moreover it has been observed, at each experi- 15 indicate; amongst others a particular method gient wlaich gage rise to a c t n eous evol 0 car ng ou e process in ques ion consiston pro uce y t e action of a basic and oxiing in violently pouring the metal in a large dizing Slag HDOII p iron a S 1 d which jet upon the molten slag placed at the botto produced itself a certain seething ensuring an of a ladle, the violence of the pouring being t mi s of t m a a d of the s a t at 20 such that it produces the pulverization of the o this fact more 01' less considerable but slag and its emulsification in the metal. i always appreciable dephosphorization is obtained Now the applicant has observed during experiaccording 11:0 the greater or less intensity of ments upon pig iron and hard steels with the Seething W 0h s produced.

use of basic oxidizing slags th t h ii; i at- The analysis of these results led the applicant 25 tempted to cause the metal to act upon the slag to the following theory. with an energy such as that employed in the t i en hlereis cause}? to! acltl 1113(1)? a carbugized process of the above mentioned patent, for ex 5 e6 D8 Iron P p 118, a 8.810 ample by violent pouring of the metal upon th oxidizing slag, two main reactions are produced,

slag in a receptacle, there is produced, as a the reduction of the iron oxide by the carbon 30 sequence of an extremely copious gaseous evoiu- 9 the bath, and the combined reaction D tion, an explosive reaction involving the projecthe phosp u O t s O de a d 0f t e a e of tion of a part or even of the whole of the metal a l-: t f th t C+F o CO+F and of the sla out of the rece tacle. e 0 e59 mac lonse when on E contrary metal is caused gives rise to the evolution of carbon monoxide 35 to act upon the slag without imparting conand it is this which produces the seething. The sdemble energy f f',; ,fi ifififfiiifltffi ff iie'iliitfiiofitifiiiifieLE2? o the metal rela ive y s ow upon e sla g rfd by interrupting the pouring from t and of the Foo content, or more exactly of the 40 to time, there is still obtained a gaseous evoludisparity existing between the contents of these 40 tion but this no longer involves the projection elements at the'moment of placing the metal of the metal and of the slag out of the rece? and the slag into contact and the final contents tame but produces, however, a sumcient inter when equilibrium is established; but it evidently also depends upon the pressure of CO according mixing of the slag and of the metal by pro ech t H t th b d f th I to the law of mass action. The fact that the F101] 01' t 9 me a n o e y o e s removal of the gas evolved cannot be instanta- The applicant has studied' neous thus slows down the reactionby creating what was the thls phenomenon an opposing pressure of CO and limits the reacand under What It was l tion. When the evolution of gas is finished, this In What cases and by means of What opposing pressure ceases and the reaction may 50 The second reaction, which is the well known reaction of dephosphorization by formation of phosphoric acid and then of basic phosphate, for example calcium phosphate, does not itself involve any formation of gas. Its speed is thus controlled solely by the disparity with respect to equilibrium of the contents of the reacting elements of the metal and of the slag, by the extent of the slag-metal contact, and by the speed of difiusion, it is not subject to the same cause of slowing down as the first reaction.

The fundamental idea of the applicant resides precisely in the utilization of the difference of speed existing between these two reactions, employing the first not to obtain considerable decarburization but simply to obtain a sufiiciently intense seething and consequently an int'ermixing of the metal and of the slag, leading to the rapid development of the second reaction and on the other hand in the control of the reaction of explosive species thus produced, so that there takes place a violent seething without however there being a risk of explosion.

According to the present invention the dephosphorization will be efiected by the action upon the metal of a molten basic and oxidizing slag of such composition and at such a temperature that the iron oxide of the slag is reduced by the carbon of the bath, and so that there is produced by intense evolution of carbon monoxide a seething producing intermixing of the metal and of the slag and consequently ensuring rapid dephosphorization of the metal.

The necessary seething may be produced in particular by causing the metal to act upon the slag with an energy which is sufficient to initiate the reaction of seething and to ensure a suflicient intermixing but which is not such that the said reaction becomes explosive.

It should be observed that the operation, in spite of the formation of CO which is produced, does not modify to a very substantial extent the carbon content of the metal, for it is sufficient that a very small quantity of carbon shall be oxidized in order to develop, at the temperatures in view, a very considerable volume of gas and one sufiicient to produce an intense seething.

Obviously the slag intended for a determined metal should be chosen with a composition suitable for eliminating phosphorus, that is to say basic and oxidizing. When the metal contains besides phosphorus, other more oxidizable elements such for example as silicon, the quantity of slag to be employed and its iron oxide content should be chosen so that after oxidation of these elements the slag maintains a sufficiently basic and oxidizing character to be able to dephosphorize to the extent desired.

A preferred method of carrying out the process which forms the subject of the invention consists in pouring, ingeneral without violence, the metal upon the molten slag placed at the bottom of a ladle. It has been observed according to the invention that by suitably adjusting the height from which the metal is poured and the speed of pouring, and, if desired, by interrupting from time to time the pouring of the metal, there may be obtained in the ladle a seething the violence of which is not such that the metal and the slag are projected out of the ladle, but which is however energetic enough to produce by the effect of the slag-metal intermixing a very considerable dephosphorization.

Obviously the method of carrying out the pouring, the speed of pouring, and the height from which the metal falls should be adapted to the more or less oxidizing character of the slag, to the higher or lower carbon content of the metal, as well as to the temperature. It is suitable in general to pour the metal in a rather thin jet and from a less height than that corresponding to the method of violent pouring disclosed in particular in Patent No. 2,015,692 mentioned above, but this height should still be relatively considerable, for it is necessary that the metal when falling into the slag should entrain a small part thereof so that the reaction of seething may be initiated. 'If the pouring is not carried out from a suflicient height or is performed too slowly, the

metal will pass under the slag without producing considerable gaseous reaction, there will not be projection of the metal into the slag and the dephosphorization will be very small.

To sum up, the method of operation of pouring the metal upon the slag should be maintained in an intermediate zone between;-too rapid a pouring, which would only lead to expelling the metal and the slag from the receptacle;too slow a pouring, or pouring from too small a height, which would give an insufficient gaseous evolution to project the metal violently into the slag and to obtain sufficient contact.

An advantageous 'method of operation consists in first pouring the metal into a ladle, and in the pouring it from the bottom of this ladle interrupting if desired the pouring if the seething becomes too violent and a danger arises of the ladle of slag overflowing.

The process according to the invention finds an application of particular interest in the dephosphorization of acid Bessemer steel. The Bessemer.

steel is first worked up in the usual manner by blowing until an extra mild steel is obtained, then the metal is recarburized and the desired additions of ferromanganese are made thereto, then the dephosphorization of thisrecarburized metal is carried out according to the process which forms the subject of the application, by causing to act upon the said metal so as to produce seething, a suitable dephosphorizing slag, for example by slowly pouring the metal into the said slag which has been previously melted.

In this case, the metal containing manganese, it will be of interest, so that this manganese is not uselessly oxidized, to add to the basic dephosphorizing slag manganese oxide, MnO or M11304. By calculation and experiment the quantity of these oxides to be added will be determined, so that after the operation the Mn content is not lowered, which implies that after the operation the ratio MnO FeO has a value superior or equal to KMnXMn, Kun being the well known constant of manganese and Mn the initial manganese content. The constant referred to (KMn) is the constant defined by the relation:

invention may likewise be applied to blast furnace pig iron. To preserve the manganese of the latter, if desired an addition of manganese may be made in the slag. In the case when the pig iron contains silicon a quantity of slag will be added such, and having such a content of MnO or other bases, that in spite of the enrichment of the slag in silica the slag will remain definitely basic till the end of the operation.

It has been recognized that by causing a basic and oxidizing slag to act upon blast furnace pig iron under conditions according to the process forming the' subject of the invention, for ex.- ample by cautiously pouring the metal upon the said slag, a. violent intermixing is obtained ensuring rapid dephosphorization without however causing the contents-of the receptacle to overflow.

In the following there is given an example of carrying out the process according to the invention applied to the dephosphorization of a pig iron. 4 l a A ladle containing 500 kgs. of a pig iron with Percent Carbon 3.,3 Silicon I I 0.300 Phosphorus 0. 120 Manganese 1. 1

was slowly poured from a height of 3 metres into a ladle containing about 60 kgs. of a slag of the following composition.

Astrong seething was produced during the whole of the pouring which was carried out in a regular manner and theduration of which was about a minute and a half. A little after the termination of the poiu'ing the seething calmed down and then stopped completely.

The metal then had the following analysis;

Percent C--- 3. 080 Si 0. 050 P 0. 022 Mn 0. 9

The carbon content of the metalwas thus lowered from 3.30% to 3.08% besides the content of silicon from 0.030% to 0.005%. The phosphorus content fell from 0.120% to 0.022% that is a dephosphorization of 18.33%.

The analysis of the slag after the operation was the following:

Percent FeO g 5. 3 S102; 29 (19.0 48 MnO 13 P205 2 A1203"--- 0. 9 MgO 1.8

What 1 claim is: p 1. A process for dephosphorizing acid Bessemer steel by means of an oxidizingbasic slag, which consists in adding to the steel a metallic substance of the group comprising manganese and ferromanganese and then pouring with such care the molten steel into a ladle containing the molten slag at such a temperature and with such a content of iron oxide that said iron oxide in the slag is reduced by carbon in the steel so as to produce,

with the formation of carbon monoxide a seething which is sufficiently active to cause intermixing of the steel and of the slag and thereby a rapid dephosphorization of the said steel but not so intense as to cause the contents of the ladle oxide takes place resulting in the production of a seething layer of the slag permeated by carbon monoxide bubbles into which layer metal particles are projected upwards from the underlying metal, leading to an almost complete intermixing of the metal and the slag and thereby to a rapid depho'sphorization of said metal. RE E .PERRIN. 

